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#11
If you bought from a retail outlet then it may have a product key. That is one of the few ways to get a product key. If you bought from the Microsoft Store online and ordered the usb then I don't think it will have a product key. Microsoft is using digital entitlement in most scenarios and no product key is provided. A product key does appear in the system after installation. Digital entitlement works very differently than the traditional (and now disappearing) product key.
If you bought the full product package (FPP), called by Microsoft "Standalone copy", Windows 10 won't rely on any previous version of Windows, even if you choose to upgrade a Windows 7 or 8 installation. Only the free Get Windows 10 (GWX) upgrades require a previous version of Windows.
In general, the only legacy product keys that can be used to activate Windows 10 (in the free GWX scenario) are Windows 7 and 8 from the same computer you are installing 10 on or keys not used to activate another computer. I say "in General" because not all possible scenarios have been reported on. So if your Windows 7 and 8 keys are what you used to activate other computers you are still using you probably will not be able to use them again with Windows 10. I have tried it and it does not work.
It all depends on that Windows 10 "box" you have at home.
Here is a Microsoft document that explains when digital entitlement is used and when a product key are provided when you get Windows.
Activation in Windows 10 - Windows Help